Rendering specific colors from color printing systems can vary over time, and sometimes within a single job. In addition, environmental conditions, such as humidity and temperature, greatly affect toner and a particular system's print capabilities. The degree to which a particular color can vary and still be acceptable can differ based on a number of factors, such as, for example, the requirements of the customer, the specific job being printed, the print shop handling the print job, the specific color being printed, etc. Print shops that require a high degree of color fidelity typically inspect the printed job output at some specified interval. These inspections are often visual, but may also include measurement devices.
FIG. 1 shows a schematic illustration of a xerographic printing system 100, such as the Xerox Corp. iGen4® Digital Production Press. The print system 100 includes a source of paper or printable substrates 102 that is operatively connected to a printing engine 104, and output path 106 and finisher 108. As illustrated, the print engine 104 is a multi-color engine having a plurality of imaging/development subsystems 110 that are suitable for producing individual color images (e.g., CMYK) on belt 114, where the belt then transfers the images to the substrate.
Presently color spectral measurements in the iGen4® are made with the an in-line spectrophotometer (ILS) 120 mounted on the main paper path located in the output path 106. Because of this configuration, the customer typically has to run a dedicated print job to make spectral measurements, which requires additional print time and reduces efficiency.
In addition, in conventional printers where the ILS measures the ink/toner only a few seconds after fusing, this may result in inaccurate color measurements due to a phenomenon known as thermo chromaticity. Thermo chromaticity is a change in perceived color of an ink or toner as it changes temperature. Because of the fuser device in printers, prints are warm to touch as they are generated in a copier/printer and take some time (e.g., 10s to 100s of seconds) to cool to room temperature after they are printed.
The temperature of the ink or toner of prints has been measured as much as 110-120° F. As the ink/toner cools to room temperature (approximately 70° F.), its color may noticeable change. Color shift has been measured as much as 6 delta-E 2000.